How can i add more duplicates to a curve?
You can adjust the amount and density of dupliframes from two different parameters.

Adjust the density of duplicated objects from the number of Frames in the Curve Object data > Path Animation > Frames*. A higher number will yield a denser amount of duplicated objects.

If increasing the value high enough gives too few objects to fill the whole curve, then select the duplicated object and under Object > Duplication increase the End Time value so it fills the whole curve again.